Labels: text | font OCR: The first argument to open( ) is a file name; the second argument specifies how the file is to be opened. If there are no errors, the function returns a file descriptor; otherwise, the value -1 is returned. The identifier in_fd is mnemonic for "in file descriptor." On our system, the symbolic constant O_RDONLY is given in fcntl.h. It is mnemonic for "open for reading only.'